The present invention relates to processes for the production of methyl dithiocarbazinate (MDTC). More particularly, in invention relates to processes for the production of methyl dithiocarbazinate which comprise the steps of providing a mixture comprising hydrazine, solvent, carbon disulfide and base; adding methyl bromide to form a reaction mixture; cooling the reaction mixture; and recovering methyl dithiocarbazinate. The present invention further relates to processes of recovering MDTC from a reaction mixture comprising the steps of filtering the reaction mixture to yield a solid MDTC retentate and a liquid filtrate; acidifying the filtrate; and adding methyl isobutylketone to the acidified filtrate.
Methyl dithiocarbazinate may serve as a reactant or intermediate in the preparation of useful compounds. For example, Le, U.S. Pat. No. 4,696,938, discloses a process for preparing and using methyl hydrazinecarbodithioate as a reactant in the preparation of 6-aryl-pyridine thiosemicarbazones. Le teaches that methyl dithiocarbazinate is prepared by adding hydrazine hydrate to a cooled solution of potassium hydroxide in water and 2-propanol, adding pre-cooled carbon disulfide while maintaining the internal temperature below 10xc2x0 C., stirring for a further one hour and adding cooled methyl iodide.
Mayes, U.S. Pat. No. 5,861,526, discloses a process for preparing MDTC by reacting carbon disulfide and hydrazine in the presence of a non-alcoholic solvent to form hydrazinium dithiocarbazinate and methylating said hydrazinium dithiocarbazinate with methyl bromide. Mayes teaches that the reaction of carbon disulfide and hydrazine is conducted in the presence of a non-alcoholic solvent to reduce dithiocarbazinate buildup, and that the molar ratio of solvent to carbon disulfide is from about 0.4:1 to about 3:1.
Wasleski et al., U.S. Pat. No. 5,877,339, disclose a process for preparing MDTC by reacting carbon disulfide and hydrazine in an aqueous medium in an effective ratio to form a hydrazinium dithiocarbazinate, and, without isolating the hydrazinium dithiocarbazinate, methylating the hydrazinium dithiocarbazinate in the same aqueous medium with methyl bromide. Wasleski et al. teach that the aqueous medium is selected from the group consisting of water and a mixture of water and an aprotic solvent, provided that when said aqueous medium is a mixture of water and an aprotic solvent, the aprotic solvent is used in a molar ratio of from about 0.15 to 1 mole per mole of carbon disulfide.
Jackman et al., U.S. Pat. No. 6,025,514, disclose a process for preparing MDTC by reacting carbon disulfide, hydrazine and an adjunct base in an aqueous reaction medium to form a dithiocarbazinate salt, and methylating the dithiocarbazinate salt with methyl bromide. Jackman et al. teach that the base is added in such a manner that the pH of the reaction mixture is maintained between about 8 and about 14; that the mole ratio of carbon disulfide to hydrazine to base falls in the range of (1 to 1.2):(1 to 1.2):(1 to 1.2); and that the aqueous reaction medium is selected from the group consisting of water and a mixture of water and a non-alcoholic hydrocarbon solvent.
Unfortunately, many prior art processes produce MDTC in unsatisfactory yield and purity, or require the use of relatively expensive alkylating agents, such as methyl iodide. Thus, there is a need in the art for a process for producing MDTC in high yield and purity, and which preferably employs methyl bromide as an alkylating agent. Further, there is a need for a process of recovering MDTC from a reaction mixture. Preferably the MDTC recovery process renders any resulting aqueous waste non-biotoxic and suitable for normal waste disposal.
Accordingly, it is an object of the present invention to obviate problems of the prior art. It is a further object of the present invention to provide processes for the production of MDTC in high yield and/or high purity. It is yet an additional object of the invention to provide for methods for the recovery of MDTC from the reaction mixture, and processes of treating the aqueous waste formed during the production of MDTC. These and additional objects are provided by the processes of the invention.
According to one aspect of the invention there are provided processes for the production of MDTC comprising the steps of mixing hydrazine with a solvent to form a mixture; adding carbon disulfide to the mixture; adding a base to the mixture after the addition of carbon disulfide is started; adding methyl bromide to the mixture after the addition of the carbon disulfide and base is completed; keeping the resultant reaction mixture at a temperature of from about 5xc2x0 C. to about 40xc2x0 C. for a period of from about 30 minutes to about 2 hours; cooling the reaction mixture to a temperature of from about 0xc2x0 C. to about 15xc2x0 C., and maintaining the reaction mixture at that temperature range for a period of from about 15 minutes to about 2 hours; and recovering MDTC. The solvent may be selected from the group consisting of water and a mixture of water and a non-alcoholic hydrocarbon solvent.
According to another aspect of the invention there are provided methods of recovering MDTC comprising the steps of filtering the reaction mixture to yield a solid MDTC retentate and a liquid filtrate; acidifying the filtrate with a mineral acid; and adding methyl isobutylketone to the acidified filtrate.
According to one aspect of the invention there are provided processes for the production of MDTC comprising the steps of providing a mixture comprising hydrazine and solvent; adding carbon disulfide to the mixture; after the carbon disulfide addition is completed then adding base to the mixture; after the base addition is completed then adding methyl bromide to the mixture; keeping the reaction mixture at a temperature of from about 5xc2x0 C. to about 40xc2x0 C. for a period of from about 30 minutes to about 2 hours; cooling the reaction mixture to a temperature of from about 0xc2x0 C. to about 15xc2x0 C., and maintaining the reaction mixture at that temperature range for a period of from about 15 minutes to about 2 hours; and recovering methyl dithiocarbazinate from the reaction mixture.
According to another aspect of the invention there are provided processes for the production of MDTC comprising the steps providing a mixture comprising hydrazine, solvent, carbon disulfide and base; adding methyl bromide to the mixture thereby forming a reaction mixture; cooling the reaction mixture to a temperature of from about 0xc2x0 C. to about 15xc2x0 C., and maintaining the reaction mixture at that temperature range for a period of from about 15 minutes to about 2 hours; and recovering MDTC.
The processes of the invention of the invention are advantageous in that MDTC may be produced with high yield (from about 89% to about 91%) and/or high purity (about 95%). Additionally, the aqueous waste formed during the MDTC production can be rendered non-biotoxic.
These and additional aspects, objects and advantages of the invention are more fully described in the following detailed description.
The process for the preparation of MDTC using base, hydrazine, carbon disulfide and methyl bromide can be represented as set forth below: 
As used herein, xe2x80x9cbasexe2x80x9d refers to a basic compound other than the hydrazine reactant. The hydrazine is preferably hydrazine hydrate.
In one embodiment of the invention, methyl dithiocarbazinate is prepared by providing a mixture comprising hydrazine, solvent, carbon disulfide and base; adding methyl bromide, thereby forming a reaction mixture, keeping the reaction mixture at a temperature of from about 5xc2x0 C. to about 40xc2x0 C., preferably from about 20xc2x0 C. to about 30xc2x0 C., for a period of from about 30 minutes to about 3 hours, preferably from about 1 to about 2 hours; cooling the reaction mixture to a temperature of from about 0xc2x0 C. to about 15xc2x0 C., and maintaining the reaction mixture at that temperature range for a period of from about 15 minutes to about 2 hours, preferably from about 1 to about 1.5 hours, and recovering methyl dithiocarbazinate from the reaction mixture. The MDTC may be recovered and any aqueous waste treated by filtering the reaction mixture to yield a solid MDTC retentate and a liquid filtrate; acidifying the filtrate, preferably with a mineral acid; and adding methyl isobutylketone to the acidified filtrate.
In a further embodiment, the mixture comprising hydrazine, solvent, carbon disulfide and base may be provided at a temperature of no greater than about 30xc2x0 C., such as, for example, a temperature in the range of from about 5xc2x0 C. to about 30xc2x0 C. or in the range of from about 10xc2x0 C. to about 40xc2x0 C. The methyl bromide may be added over a period of time, such as from about 1 hour to about 4 hours, during which the resulting mixture is at a temperature of no greater than about 40xc2x0 C., such as, for example, a temperature in the range of from about 5xc2x0 C. to about 40xc2x0 C.
The mixture comprising hydrazine, solvent, carbon disulfide and base may be prepared in a simultaneous add or consecutive add manner. As used herein xe2x80x9csimultaneous addxe2x80x9d refers to the substantially simultaneous addition of carbon disulfide and base to a mixture comprising hydrazine and solvent. As used herein xe2x80x9csubstantially simultaneous additionxe2x80x9d is intended to mean the carbon disulfide add may have a lead time of from about 5 to about 20 minutes. The step of adding carbon disulfide and base to the mixture comprising hydrazine and solvent may be performed at a temperature of no greater than about 30xc2x0 C., such as, for example, a temperature in the range of from about 10xc2x0 C. to about 30xc2x0 C., over a time period of from about 1 hour to about 4 hours, preferably from about 2 to about 3 hours.
In a further embodiment of the simultaneous add approach, a reactor vessel is charged with solvent and hydrazine, and carbon disulfide and base are added to a mixture of a solvent and hydrazine. The carbon disulfide add has a lead time of about 15 minutes. The carbon disulfide and base are added to the mixture at a temperature of from about 10xc2x0 C. to about 30xc2x0 C., preferably from about 25xc2x0 C. to about 30xc2x0 C., over a time period of from about 1 hour to about 4 hours, preferably from about 2 hours to about 3 hours. Following the addition of the carbon disulfide and base, methyl bromide is added to the resulting reaction mixture at a temperature of from about 5xc2x0 C. to about 40xc2x0 C., preferably from about 25xc2x0 C. to about 30xc2x0 C., over a time period of from about 1 hour to about 4 hours, preferably from about 2 hours to about 3 hours.
As used herein xe2x80x9cconsecutive addxe2x80x9d refers to mixing hydrazine with a solvent; adding carbon disulfide to the mixture of hydrazine and solvent; and adding a base after the addition of carbon disulfide is completed. The step of adding the carbon disulfide to the mixture of hydrazine and solvent may be performed at a temperature of no greater than about 30xc2x0 C., such as, for example, a temperature in the range of from about 5xc2x0 C. to about 30xc2x0 C., over a time period of from about 1 hour to about 4 hours, preferably from about 2 to about 3 hours. The step of adding the base may be performed at a temperature of no greater than about 30xc2x0 C., such as, for example, a temperature in the range of from about 5xc2x0 C. to about 30xc2x0 C., over a time period of from about 1 hour to about 4 hours, preferably from about 2 to about 3 hours.
In a further embodiment of the consecutive add approach, a reactor vessel is charged with solvent and hydrazine. Carbon disulfide is then added to the mixture of solvent and hydrazine at a temperature of from about 5xc2x0 C. to about 30xc2x0 C. over a time period of from about 1 hour to about 4 hours. Following the addition of the carbon disulfide, a base is added to the mixture at a temperature of from about 5xc2x0 C. to about 30xc2x0 C. over a time period of from about 1 hour to about 4 hours. After the base has been added, methyl bromide is added to the reaction mixture at a temperature of from about 10xc2x0 C. to about 40xc2x0 C. over a time period of from about 1 hour to about 4 hours.
The carbon disulfide, hydrazine, base and methyl bromide are used in amounts sufficient for the desired reactions to occur. In one embodiment of the invention the carbon disulfide is present in the reaction mixture in an amount such that the molar ratio of carbon disulfide to hydrazine is from about 1.00:1 to about 1.08:1; and preferably about 1.04:1. The molar ratio of carbon disulfide to base is from about 1.04:1 to about 1.1:1; preferably about 1.08:1. The molar ratio of carbon disulfide to methyl bromide is from about 1.1:1 to about 1:1.1, preferably about 1:1.
The reaction is conducted in a pH range that does not adversely affect the reaction. Typically, the reaction may be conducted in a pH range of from about 8 to about 14, preferably from about 9 to about 14. The pH can be controlled by the rate at which the base is added. Generally the base is added slowly over a period of time.
Suitable bases for use in the processes of the present invention include inorganic bases, such as alkali metal and alkaline earth metal hydroxides, and nitrogenous bases, such as ammonia, ammonium hydroxide and amines. Suitable inorganic bases include sodium hydroxide, potassium hydroxide, lithium hydroxide and calcium hydroxide, while suitable amines include ethanolamine, di-n-propylamine, di-isopropylamine, di-n-butylamine, t-butylamine, dimethyl benzylamine, ethylmethyl pyridine, and methanediamine. In an embodiment of the invention, the base is sodium hydroxide. The sodium hydroxide may be in the form of a aqueous solution, such as 25%, by weight, aqueous sodium hydroxide.
Suitable solvents for use in the present invention include water, non-alcoholic hydrocarbon solvents, and mixtures thereof. The non-alcoholic hydrocarbon solvents include aromatic solvents such as benzene, toluene, xylene and ethyl benzene; and aliphatic solvents such as pentane, hexane, cyclohexane, and heptane. Preferred solvents include toluene. In one embodiment of the invention the solvent is a mixture of water and a non-alcoholic hydrocarbon solvent in a weight ratio of from about 1:2 to about 1:4. In one embodiment to solvent is free of alcohol.
Processes in accordance with the present invention do not require, and are preferably free of, methyl iodide. However, if desired a catalyst, such as a phase-transfer catalyst can be employed in the reaction(s). An example of the catalyst is tris-[2-(2-methylethoxy) ethyl]amine (TDA-1), N-benzyltrimethylammonium hydroxide, N-methylimidazole, dimethylamino-pyridine, 1,4-diazabicyclo-(2,2,2)-octane and diethylene glycol. The mole ratio of the catalyst can be 0 to 100 mmoles, preferably 0 to 1 mmoles, per mole of carbon disulfide.
Processes in accordance with the present invention require no isolation of intermediate dithiocarbazinate salts. Thus, in one embodiment of the invention, the reaction is conducted in a one pot process without separation or isolation of an intermediate product. However, though not required, intermediate dithiocarbazinate salts may be isolated if desired.
The MDTC may be recovered from the reaction liquor by separation methods such as, for example, centrifugation or filtration. In one embodiment the reaction mixture is filtered to yield a solid MDTC retentate and a liquid filtrate. The MDTC is allowed to air dry. The liquid filtrate, which generally comprises aqueous waste, is acidified, preferably with a mineral acid, and methyl isobutylketone is added to the acidified filtrate. Generally the methyl isobutylketone to aqueous waste volume ratio is from about 1:3 to about 1:10, preferably about 1:5. The methyl isobutylketone may then be removed, and the remaining water may be adjusted to a positive redox potential with sodium hypochlorite and then subjected to normal water disposal.
Suitable mineral acids for acidifying the liquid filtrate include hydrochloric acid, sulfuric acid and phosphoric acid, preferably the acid in sulfuric acid. Generally the aqueous waste is acidified to a pH of from about 5 to about 7, preferably to a pH of from about 5 to about 6.
The processes according to the present invention provide a MDTC yield of from about 89% to about 94%, preferably from about 91% to about 93%, and a MDTC purity of from about 93% to about 97%, preferably from about 94% to about 95%.
Throughout the examples and the present specification, parts and percentages are by weight unless otherwise specified. The following example is illustrative only and is not intended to limit the scope of the methods and fabrics of the invention as defined by the claims.